1. Field of the Invention
The present invention relates to tool holder attachment structures that attach a tool holder provided with a cutting tool to a rotary spindle of a machine tool such as a machining center with an automatic tool changer, and tool holders that are attached to the rotary spindle.
2. Background Art
Such a tool holder attachment structure is disclosed in, e.g., Japanese Patent No. 2571325. FIG. 4 is a diagram corresponding to FIG. 5 of Japanese Patent No. 2571325, and shows a structure in which a tool holder is attached to a spindle of a machine tool.
In a tool holder 3 for use in a machining center with an automatic tool changer, a manipulator holding flange 5 for automatic tool changing is formed integrally with the tool holder 3 so as to adjoin a tapered shank portion 4. A tapered hole 2 is provided in a spindle 1 of a machine tool, and the tool holder 3 is drawn into the tapered hole 2 and is clamped therein by using a pull stud bolt.
The JIS or ISO standards specify the maximum diameter D, the axial length (reference dimension) L, etc. of the tapered hole 2 and the tapered shank portion 4, and specify that a predetermined opposing clearance Y should be provided between a reference end face 1a of the spindle 1 and an end face 5a of the flange 5 of the tool holder 3 in order to allow for a certain degree of manufacturing error Δi.
With this configuration, even if the reference end face 1a or the flange end face 5a protrudes slightly toward the opposing end face due to a manufacturing error, the reference end face 1a does not contact the flange end face 5a due to the predetermined opposing clearance Y, and the tapered shank portion 4 can be reliably closely fitted in the tapered hole 2.
However, this configuration has a disadvantage in that the close contact surfaces of the tapered hole 2 and the tapered shank portion 4 tend to be worn due to fretting corrosion etc. because the tapered shank portion 4 is intensively subjected to cutting load.
One way to overcome this disadvantage is to extend the reference end face 1a of the spindle 1 or the flange end face 5a so as to protrude by the opposing clearance Y so that the tapered shank portion 4 is closely fitted in the tapered hole 2 and the reference end face 1a closely contacts the flange end face 5a. However, the opposing clearance Y is provided so as to allow for the manufacturing error Δi. Therefore, if, e.g., the end face of the spindle 1 slightly protrudes by the amount of the manufacturing error, the end face of the spindle contacts the flange end face of the tool holder before the tapered shank portion 4 is closely fitted in the tapered hole 2, leaving a gap between the tapered hole 2 and the tapered shank portion 4. As a result, the tool holder cannot be reliably attached to the spindle.
The invention described in Japanese Patent No. 2571325 proposes the following configuration in order to solve the above problems. Each of the spindle end face and the flange end face facing the spindle end face is extended by an amount larger than the numerical value of the allowable manufacturing error Δi specified in the industrial standards. Moreover, the spindle end face and the flange end face are extended toward each other so that the sum of the extension amounts α1, α2 of the spindle end face and the flange end face is within the range of the numerical value of the allowable opposing clearance Y. The tool holder 3 can be attached to the spindle 1 so that the extended end faces thus formed are fitted on each other.